Watercress (Nasturtium officinale) is a native European perennial plant which since introduced into Japan in the early Meiji era, has produced colonies in a clear stream as a naturalized plant, and it is eaten mainly as an ornamental accompaniment for Western cooking and as a vegetable for salads.
An attempt at blending various solvent extractions of plants including this watercress with external preparations such as cataplasms, ointments etc. is disclosed in Japanese Laid-Open Patent Application No. 7-25763. This publication describes that the combined use of kojic acid and/or its derivative having an inhibitory action on melanin formation and various plant extracts, brings about the effect of improving the persistent efficacy of kojic acid and/or its derivative while alleviating irritation on the skin. Under the present circumstances, however, it is not sufficiently examined whether the solvent extract of watercress when blended in the external preparations has the humectant effect or any other effects.
In recent years, as the house and office come to be completely furnished with air conditioners and by excess use of a soap or detergent, there are increasing skin troubles such as rough skin, itching etc. Against such symptoms, lotions or ointments containing urea or aloe extract etc. are commercially available as external preparations for efficiently maintaining the water content of the skin or giving the humectant effect. However, no adequate examination has been made of plant extract-blended external preparations excellent in the sense of use.
Meanwhile, calefacients such as powdered capsicum, capsicum extract, capsicum tincture, nonanoic acid vanillylamide etc. are known for a long time. If these calefacients are applied to the skin, the sense of heat is generated at the application site, blood capillaries are expanded to make blood circulation active to improve the metabolism of tissues, and demonstrate the anti-inflammatory and analgesic effects. Accordingly, there appeared the products containing these calefacients in cosmetics to utilize these effects or in medical external preparations the purpose of treating neuralgia, stiffshoulder, lumbago, rheumatism and so on.
However, when external preparations containing these calefacients are applied to the skin, there is a considerable difference in the degree in sense of heat, depending on the age, sex, application site and the individual conditions. Further, if the calefacient is contained in a large amount, it may cause the uncomfortable symptoms of skin irritation such as redness, rashes etc., therefore, it is difficult to determine the optimum concentration of the calefacients. Furthermore, if the calefacient is blended with plasters, the sense of irritation remains even after removal of the plasters, and severe pain is frequently experienced at the time of bathing.
To solve such problems, there is an attempt to give the mild sense of heat to the skin by using the herb medicines such as ginger, Japanese pepper etc. (see Japanese Patent Publication No. 56,206/1988). The other attempt is to relieve the irritation by containing perilla or yellow oak extract together with the calefacients (see Japanese Patent Publication No. 51,126/1988). However, even if these herb ingredients are contained, it cannot be said that the effect of reducing skin irritation while keeping the sense of heat is sufficient, so there is demand for further development.
Accordingly, in view of these circumstances, the object of the present invention is to provide external preparations containing herb ingredients, which are excellent in the humectant effect, capable of reducing the uncomfortableness of irritation even if calefacients are contained, and able to give a comfortableness of use to the user.
To solve the above mentioned problems, the present inventors extensively studied the humectant effect, and skin irritation relieving effect and the other effects of said preparations containing the herb ingredients. As a result, they found that external preparations containing solvent extract of watercress gives humectant to the skin, facilitates the sense of heat when calefacients are further contained, and hardly permit the calefacients to cause skin pain. Hence, the present inventors arrived at the completion of the present invention.